Kermode H, Williams A J, Sitsapesan R
Imperial College School of Science, Technology and Medicine, Cardiac Medicine, London, United Kingdom.
Biophys J. 1998 Mar;74(3):1296-304. doi: 10.1016/S0006-3495(98)77843-9.
The effects of ATP, ADP, and inorganic phosphate (Pi) on the gating of native sheep cardiac ryanodine receptor channels incorporated into planar phospholipid bilayers were investigated. We demonstrate that ATP and ADP can activate the channel by Ca2+-dependent and Ca2+-independent mechanisms. ATP and ADP appear to compete for the same site/s on the cardiac ryanodine receptor, and in the presence of cytosolic Ca2+ both agents tend to inactivate the channel at supramaximal concentrations. Our results reveal that ATP not only has a greater affinity for the adenine nucleotide site/s than ADP, but also has a greater efficacy. The EC50 value for channel activation is approximately 0.2 mM for ATP compared to 1.2 mM for ADP. Most interesting is the fact that, even in the presence of cytosolic Ca2+, ADP cannot activate the channel much above an open probability (Po) of 0.5, and therefore acts as a partial agonist at the adenine nucleotide binding site on the channel. We demonstrate that Pi also increases Po in a concentration and Ca2+-dependent manner, but unlike ATP and ADP, has no effect in the absence of activating cytosolic [Ca2+]. We demonstrate that Pi does not interact with the adenine nucleotide site/s but binds to a distinct domain on the channel to produce an increase in Po.
研究了三磷酸腺苷（ATP）、二磷酸腺苷（ADP）和无机磷酸盐（Pi）对整合到平面磷脂双分子层中的天然绵羊心脏兰尼碱受体通道门控的影响。我们证明，ATP和ADP可通过依赖钙离子（Ca2+）和不依赖Ca2+的机制激活该通道。ATP和ADP似乎竞争心脏兰尼碱受体上的同一位点，并且在胞质Ca2+存在的情况下，两种试剂在超最大浓度时都倾向于使通道失活。我们的结果表明，ATP不仅对腺嘌呤核苷酸位点的亲和力比ADP大，而且具有更高的效能。ATP激活通道的半数有效浓度（EC50）值约为0.2 mM，而ADP为1.2 mM。最有趣的是，即使在胞质Ca2+存在的情况下，ADP也不能使通道的开放概率（Po）激活到0.5以上，因此在通道上的腺嘌呤核苷酸结合位点充当部分激动剂。我们证明，Pi也以浓度和Ca2+依赖的方式增加Po，但与ATP和ADP不同，在没有激活胞质[Ca2+]的情况下没有作用。我们证明，Pi不与腺嘌呤核苷酸位点相互作用，而是与通道上的一个不同结构域结合，从而使Po增加。
